Once you’re in private browsing mode, make sure you’re signed out of your Google Account. Follow these steps to check if you’re signed out of your browser:

Visit any Google page, like google.com.

Look in the top right corner of the page.

If you see the blue Sign in button, you’re already signed out of your account.

If you don’t see the blue Sign in button, click your photo or email address >Sign out.

Note: If you're using the Google app on your Android or iOS, you have to remove your Google Account from the app to sign out. This isn't recommended because when you remove your Google Account, things like Google Now won't work.